1. Field of the Invention
The present invention relates to luminous glass containing rare earth ions, wherein the characters of thermal expansion and mechanical strength, of the luminous glass are improved. In particular, the invention relates to the luminous glass which can be suitably applied to an oscillation medium for laser oscillation, an excitation light filter or the like.
2. Description of Related Art
For materials which are applied as the luminous materials in earlier technology, a glass material, a single crystal material, and a ceramic material have been known.
For the glass material, for example, various laser glasses such as quartz laser glass, phosphate system laser glass or the like, which contain rare earth ions and are applied to oscillation medium for laser oscillation have been known.
The luminous glass material is not only applied to the laser glass. For example, Japanese Patent Application No. 9-188543 laid open discloses blue emission glass which can be applied to; optical detector which applied to confirmation of radiation beam position such as ultraviolet beam, X-ray or the like, mode pattern recognition, spatial distribution state; an element for optical power meter; an image displaying sensor; and the like.
However, there are problems of the thermal resistance in the glass material in earlier technology. That is, because the glass material has a high coefficient of thermal expansion, when the glass material is subjected to irradiation by an excitation light with high intensity, the glass material breaks under thermal expansion thereof. When the glass material is used under such environmental circumstances, temperature of which is largely or rapidly changed, the glass material breaks under thermal fatigue thereof. Accordingly, there is a problem that the condition and circumstances, for using the glass material are limited.
Therefore, for example, it is required for the luminous glass material which is applied to the oscillation medium for laser oscillation or the wavelength conversion filter for excitation light of laser to prevent occurring large or rapid change of temperature, or to change the glass material to another one before the glass material thermally fatigues.
On the other hand, there are problems for the luminous single crystal material that it is difficult to uniformly dope the optically active elements to the single crystal material and to produce a product of the single crystal material having practically large size. It is suitable for the glass material to produce a product having large size compared with the single crystal material.
There is a problem that the ceramic material is liable to occur a light scattering caused by grain boundaries and pores, of the ceramic material, which is character there of. Therefore, it is difficult to apply the ceramic material to such an application requiring transparent luminous material.